Spec-driven development for AI coding assistants.

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OpenSpec

Supported AI Tools: ✅ Claude Code | 🔜 Cursor (coming soon) | ✅ AGENTS.md instructions

Create alignment between humans and AI coding assistants through spec-driven development. No API keys required.

OpenSpec ensures you and your AI assistant agree on what to build before any code is written. By discussing and refining specifications first, you bring determinism to AI code generation, getting exactly what you want, not what the AI thinks you might want.

Why OpenSpec?

The Problem: AI coding assistants are powerful but unpredictable. Without clear specifications, they generate code based on assumptions, often missing requirements or adding unwanted features. Teams waste time in review cycles because humans and AI aren't aligned on what to build.

The Solution: OpenSpec creates alignment BEFORE code is written:

• Human-AI Alignment - You and your AI agree on specifications before implementation
• Deterministic, Predictable Output - Clear specs lead to reliable, repeatable code generation
• Team Alignment via Spec Reviews - Everyone reviews intentions, not code surprises
• Clear Feature Scope - Know exactly what you're building—and what you're not
• Progress Tracking - See what's proposed, in progress, or completed at a glance
• Living Documentation - Specs evolve with your code as a natural byproduct
• Universal Tool Support - Works with any AI assistant (Claude Code, Cursor, and more)
• No API Keys Required - Integrates through context rules, not external services

How It Works

┌─────────────┐       ┌─────────────┐       ┌──────────────┐
│    SPECS    │       │   CHANGES   │       │   ARCHIVE    │
│   (Truth)   │◀──────│ (Proposals) │──────▶│ (Completed)  │
└─────────────┘       └─────────────┘       └──────────────┘
      ▲                      │                      │
      │                      ▼                      │
      │               ┌─────────────┐               │
      └───────────────│    CODE     │◀──────────────┘
                      └─────────────┘

1. SPECS define current capabilities (what IS built)
2. CHANGES propose modifications using deltas (what SHOULD change)  
3. CODE implements the changes following tasks
4. ARCHIVE preserves completed changes after deployment

Installation

Prerequisites

• Node.js >= 20.19.0

Install OpenSpec

Install globally:

npm install -g @fission-ai/openspec

Getting Started

1. Initialize OpenSpec in Your Project

# Navigate to your project
cd my-project

# Initialize OpenSpec
openspec init

# Select your AI tool (more coming soon!):
# "Which AI tool do you use?"
#   > Claude Code
#     Cursor (coming soon)

# This creates:
# openspec/
#   ├── specs/       # Current specifications (truth)
#   ├── changes/     # Proposed changes
#   └── AGENTS.md    # AI instructions for your tool

2. Create Your First Change

Jump straight into creating a change proposal with your AI assistant (works with Claude Code, Cursor, or any AI tool):

// Quick win - Add a simple new feature:
You: "I want to add a user profile API endpoint.
      Please create an OpenSpec change proposal for this."

AI: "I'll create an OpenSpec change proposal for the user profile API..."
    *Creates openspec/changes/add-user-profile-api/ with:*
    - proposal.md (why this feature is needed)
    - tasks.md (implementation checklist)
    - design.md (API design decisions)
    - specs/user-profile/spec.md (new requirements)

You: "The proposal looks good. Let's implement it."

AI: "Following the tasks in openspec/changes/add-user-profile-api/tasks.md:
     Task 1.1: Create user profile model..."
    *Implements each task systematically*

3. Track Your Work

# View active changes (what's being worked on)
openspec list

# Validate your changes are properly formatted
openspec validate add-2fa --strict

# After deployment, archive the completed change
openspec archive add-2fa
# This moves the change to archive/ and updates specs/

Common Commands

# Most used:
openspec list              # See what changes you're working on
openspec archive <change>  # Mark a change as complete after deployment

# Also useful:
openspec validate <change> # Check formatting before committing
openspec show <change>     # View change details

Example: How AI Creates OpenSpec Files

When you ask your AI assistant to "add two-factor authentication", it creates:

openspec/
├── specs/
│   └── auth/
│       └── spec.md           # Current auth spec (if exists)
└── changes/
    └── add-2fa/              # AI creates this entire structure
        ├── proposal.md       # Why and what changes
        ├── tasks.md          # Implementation checklist
        ├── design.md         # Technical decisions (optional)
        └── specs/
            └── auth/
                └── spec.md   # Delta showing additions

AI-Generated Spec (created in openspec/specs/auth/spec.md):

# Auth Specification

## Purpose
Authentication and session management.

## Requirements
### Requirement: User Authentication
The system SHALL issue a JWT on successful login.

#### Scenario: Valid credentials
- WHEN a user submits valid credentials
- THEN a JWT is returned

AI-Generated Change Delta (created in openspec/changes/add-2fa/specs/auth/spec.md):

# Delta for Auth

## ADDED Requirements
### Requirement: Two-Factor Authentication
The system MUST require a second factor during login.

#### Scenario: OTP required
- WHEN a user submits valid credentials
- THEN an OTP challenge is required

AI-Generated Tasks (created in openspec/changes/add-2fa/tasks.md):

## 1. Database Setup
- [ ] 1.1 Add OTP secret column to users table
- [ ] 1.2 Create OTP verification logs table

## 2. Backend Implementation  
- [ ] 2.1 Add OTP generation endpoint
- [ ] 2.2 Modify login flow to require OTP
- [ ] 2.3 Add OTP verification endpoint

## 3. Frontend Updates
- [ ] 3.1 Create OTP input component
- [ ] 3.2 Update login flow UI

Important: You don't create these files manually. Your AI assistant generates them based on your requirements and the existing codebase.

Understanding OpenSpec Files

Delta Format

Deltas are "patches" that show how specs change:

• ## ADDED Requirements - New capabilities
• ## MODIFIED Requirements - Changed behavior (include complete updated text)
• ## REMOVED Requirements - Deprecated features

Format requirements:

• Use ### Requirement: <name> for headers
• Every requirement needs at least one #### Scenario: block
• Use SHALL/MUST in requirement text

Why OpenSpec Works

OpenSpec creates alignment between you and your AI coding assistant:

1. You describe what you want to build
2. AI creates specs before writing any code
3. You review and adjust the specifications
4. AI implements exactly what was specified
5. Everyone understands what's being built through clear specs

True Interoperability: OpenSpec is designed to be universal. No API keys, no vendor lock-in. It works by adding context rules to ANY AI coding tool - whether you use Claude Code today, switch to Cursor tomorrow, or adopt the next breakthrough AI assistant. Your specs remain portable and your workflow stays consistent.

How OpenSpec Compares

vs. Kiro.dev

OpenSpec groups all changes for a feature in one place (openspec/changes/feature-name/), making it easy to track what needs to be done. Kiro spreads changes across multiple spec folders, making feature tracking harder.

vs. No Specs

Without specs, AI coding assistants generate code based on vague prompts, often missing requirements or adding unwanted features. OpenSpec ensures alignment before any code is written.

Team Adoption

Getting Started with Your Team

1. Initialize OpenSpec - Run openspec init in your project
2. Start with new features - Use OpenSpec for your next change proposal
3. Build incrementally - Each new feature adds to your spec library
4. Future capability - We're working on tools to generate specs from existing code

Tool Freedom: Your team can use different AI assistants. One developer might use Claude Code while another uses Cursor - OpenSpec keeps everyone aligned through shared specifications. Run openspec update to configure for any supported tool without affecting others.

Contributing

• Install dependencies: npm install
• Build: npm run build
• Test: npm test
• Develop CLI locally: npm run dev or npm run dev:cli
• Conventional commits (one-line): type(scope): subject

License

MIT